Our preliminary data indicate that thiabendazole (TBZ), when administered with 2,4-dinitrofluorobenzene (DNFB) with not only affects lymphoid cells, but also hemopoietic cells. These effects are seen from the level of the pluripotent stem cell to functionally differentiated members of the lymphoid, myeloid and erythroid series. Our hypothesis is that TBZ, when given in conjunction with an exogenous T-dependent antigen, promotes the production of a humoral factor(s) which affects lymphohemopoietic proliferation and differentiation. All of these effects may be the result of a single "lymphohemopoietic-stimulating factor" (LHSF), although several factors may be involved. We will initially test T-dependent antigens other than DNFB, to determine if similar effects are seen when they are administered with TBZ. Using the TdT and CFU-S assays, we will use nude mice to help determine cell types required for production of factor(s) and response to factor(s). Other appropriate models, such as W/Wv mice with macrocytic anemia, will be used to further elucidate the above. Having defined the cell types involved, we will next turn our attention to functional and preliminary biochemical characterization of factor(s). Initial efforts will be directed at defining a functionally pure factor(s) from serum, not on obtaining biochemically pure factor(s). Initial information will include heat and cold stability, charge, molecular weight and homo-\or heterogeneity of factor activity. The specific aims are geared to achieve a full understanding of the mechanism of TBZ activity and are related to our long-term goal of bringing TBZ to a human setting in immunodeficiency states, bone marrow transplantation and as an adjunct to the commonly employed cancer treatment modalities.